Modern wireless communications devices often include multiple antennas. These multiple antennas are used to improve one or more transmission and/or reception characteristics of the wireless communications device. For example, multiple antennas may be used to implement diversity and/or multiple-input-multiple-output (MIMO) techniques, which improve transmission and reception reliability and throughput. Generally, a primary antenna is used for the transmission and reception of primary transmit and receive signals, while a secondary antenna is used for the reception of secondary receive signals. These antennas may be swapped when the transmission and/or reception characteristics of the secondary antenna are better than those of the primary antenna. This may occur, for example, when a voltage standing wave ratio (VSWR) associated with the secondary antenna is lower than a VSWR associated with the primary antenna. Such functionality is facilitated by antenna swapping circuitry. Generally, antenna swapping circuitry includes a number of switching elements configured to place the various signal paths of transceiver circuitry in communication with either the primary antenna or the secondary antenna.
FIG. 1 is a functional schematic of conventional radio frequency (RF) front end circuitry 10. The conventional RF front end circuitry 10 includes a primary antenna 12A, a secondary antenna 12B, antenna swapping circuitry 14, multiplexer circuitry 16, transceiver switching circuitry 18, primary transceiver circuitry 20, secondary receiver circuitry 22, and switch control circuitry 24. The antenna swapping circuitry 14 is coupled between the multiplexer circuitry 16, the primary antenna 12A, and the secondary antenna 12B. The transceiver switching circuitry 18 is coupled between the multiplexer circuitry 16, the primary transceiver circuitry 20, and the secondary receiver circuitry 22. The switch control circuitry 24 is coupled to the antenna swapping circuitry 14 and the transceiver switching circuitry 18.
The multiplexer circuitry 16 includes a first multiplexer 16A and a second multiplexer 16B. Each one of the first multiplexer 16A and the second multiplexer 16B include a low-band node LB, a mid/high-band node MBHB, and a common node C, and are configured to pass low-band signals between the low-band node LB and the common node C, pass mid/high-band signals between the mid/high-band node MBHB and the common node C, and attenuate other signals.
The primary transceiver circuitry 20 includes low-band primary transceiver circuitry 20A and mid/high-band primary transceiver circuitry 20B. Similarly, the secondary receiver circuitry 22 includes low-band secondary receiver circuitry 22A and mid/high-band secondary receiver circuitry 22B. The transceiver switching circuitry 18 includes low-band primary transceiver switching circuitry 18A coupled between the low-band primary transceiver circuitry 20A and the low-band node LB of the first multiplexer 16A, mid/high-band primary transceiver switching circuitry 18B coupled between the mid/high-band primary transceiver circuitry 20B and the mid/high-band node MBHB of the first multiplexer 16A, low-band secondary receiver switching circuitry 18C coupled between the low-band secondary receiver circuitry 22A and the low-band node LB of the second multiplexer 16B, and mid/high-band secondary receiver switching circuitry 18D coupled between the mid/high-band secondary receiver circuitry 22B and the mid/high band node of the second multiplexer 16B.
The antenna swapping circuitry 14 includes a first pole P1, a second pole P2, a first throw T1, a second throw T2, and a number of antenna swapping switching elements SW_AS. A first antenna swapping switching element SW_AS1 is coupled between the first pole P1 and the first throw T1. A second antenna swapping switching element SW_AS2 is coupled between the first pole P1 and the second throw T2. A third antenna swapping switching element SW_AS3 is coupled between the second pole P2 and the first throw T1. A fourth antenna swapping switching element SW_AS4 is coupled between the second pole P2 and the second throw T2. The first pole P1 is coupled to the common node C of the first multiplexer 16A. The second pole P2 is coupled to the common node C of the second multiplexer 16B. The first throw T1 is coupled to the primary antenna 12A. The second throw T2 is coupled to the secondary antenna 12B.
The low-band primary transceiver circuitry 20A includes a number of duplexers DUP each including a transmit node T, a receive node R, and a common node C, power amplifier switching circuitry PA_SW, a power amplifier PA, and a number of low-noise amplifiers LNA. The power amplifier PA is coupled to the transmit node T of each one of the duplexers DUP via the power amplifier switching circuitry PA_SW. Each one of the low-noise amplifiers LNA is coupled to a receive node R of a different one of the duplexers DUP. Each one of the duplexers DUP is configured to pass transmit signals within one or more operating bands provided at the common node C to the transmit node T, pass receive signals within the one or more operating bands provided at the receive node R to the common node C, and attenuate other signals. A common node C of each one of the duplexers DUP is coupled to the low-band primary transceiver switching circuitry 18A.
The mid/high-band primary transceiver circuitry 20B similarly includes a number of duplexers DUP each including a transmit node T, a receive node R, and a common node C, power amplifier switching circuitry PA_SW, a power amplifier PA, and a number of low-noise amplifiers LNA. The power amplifier PA is coupled to the transmit node T of each one of the duplexers DUP via the power amplifier switching circuitry PA_SW. Each one of the low-noise amplifiers LNA is coupled to a receive node R of a different one of the duplexers DUP. Each one of the duplexers DUP is configured to pass transmit signals within one or more operating bands provided at the common node C to the transmit node T, pass receive signals within the one or more operating bands provided at the receive node R to the common node C, and attenuate other signals. A common node C of each one of the duplexers DUP is coupled to the mid/high-band primary transceiver switching circuitry 18B.
The low-band secondary receiver circuitry 22A includes a number of receiver filters FIL and a number of low-noise amplifiers LNA. Each one of the low-noise amplifiers LNA is coupled to a different one of the receiver filters FIL. Each one of the receiver filters FIL is in turn coupled to the low-band secondary receiver switching circuitry 18C. Further, each one of the filters FIL is configured to filter receive signals within one or more different operating bands.
The mid/high-band secondary receiver circuitry 22B similarly includes a number of receiver filters FIL and a number of low-noise amplifiers LNA. Each one of the low-noise amplifiers LNA is coupled to a different one of the receiver filters FIL. Each one of the receiver filters FIL is in turn coupled to the mid/high-band secondary receiver switching circuitry 18D. Further, each one of the filters FIL is configured to filter receive signals within one or more different operating bands.
When operating the primary antenna 12A as intended, the switch control circuitry 24 configures the antenna swapping circuitry 14 as shown in FIG. 2. Specifically, the first antenna swapping switching element SW_AS1 and the fourth antenna swapping switching element SW_AS4 are closed, while the second antenna swapping switching element SW_AS2 and the third antenna swapping switching element SW_AS3 are open. Accordingly, the common node C of the first multiplexer 16A is coupled to the primary antenna 12A and the common node C of the second multiplexer 16B is coupled to the secondary antenna 12B. Primary transmit signals provided at the common node C of the first multiplexer 16A from the primary transceiver circuitry 20 are therefore provided to the primary antenna 12A, primary receive signals from the primary antenna 12A are provided to the common node C of the first multiplexer 16A and forwarded to the primary transceiver circuitry 20, and secondary receive signals from the secondary antenna 12B are provided to the common node C of the second multiplexer 16B and forwarded to the secondary receiver circuitry 22.
When the primary antenna 12A and the secondary antenna 12B are swapped, the switch control circuitry 24 configures the antenna swapping circuitry 14 as shown in FIG. 3. Specifically, the second antenna swapping switching element SW_AS2 and the third antenna swapping switching element SW_AS3 are closed, while the first antenna swapping switching element SW_AS1 and the fourth antenna swapping switching element SW_AS4 are open. Accordingly, the common node of the first multiplexer 16A is coupled to the secondary antenna 12B and the common node C of the second multiplexer 16B is coupled to the primary antenna 12A. Primary transmit signals provided at the common node C of the first multiplexer 16A from the primary transceiver circuitry 20 are therefore provided to the secondary antenna 12B, primary receive signals from the secondary antenna 12B are provided to the common node C of the first multiplexer 16A and forwarded to the primary transceiver circuitry 20, and secondary receive signals from the primary antenna 12A are provided to the common node C of the second multiplexer 16B and forwarded to the secondary receiver circuitry 22.
From the above description, it is clear that primary transmit signals are forwarded via either the first antenna swapping switching element SW_AS1 or the second antenna swapping switching element SW_AS2 in the antenna swapping circuitry 14, while secondary receive signals are forwarded via either the third antenna swapping switching element SW_AS3 or the fourth antenna swapping switching element SW_AS4 in the antenna swapping circuitry 14. This may be problematic in some situations. Specifically, when the primary transmit signal is a low-band signal, the first antenna swapping switching element SW_AS1 and the second antenna swapping switching element SW_AS2 may generate harmonic distortion. Since the primary transmit signal is a low-band signal, one or more of these harmonics may be located within a mid/high-band receive signal that is being received simultaneously. Accordingly, this harmonic distortion may couple into a primary or secondary mid/high-band receive signal and cause problems such as desensitization of the primary transceiver circuitry 20 and/or the secondary receiver circuitry 22.
The distortion caused by the first antenna swapping switching element SW_AS1 and the second antenna swapping switching element SW_AS2 may be caused in an on-state of the switching element due to the on-state resistance RON thereof, and may be caused in an off-state of the switching element due to the off-state capacitance COFF thereof. Generally, the on-state resistance RON of a switching element is inversely proportional to the off-state capacitance COFF thereof. This is due to the structure of a switching element. Generally, a switching element includes multiple switching devices (e.g., bipolar junction transistors, field-effect transistors, or the like), which are coupled in parallel with one another. Each switching device is associated with a channel width. Providing twice the number of switching devices in a switching element will effectively double the on-state resistance RON thereof while halving the off-state capacitance COFF. Doubling the channel width of each switching device in a switching element will effectively half the on-state resistance RON while doubling the off-state capacitance COFF. Since the first antenna swapping switching element SW_AS1 and the second antenna swapping switching element SW_AS2 are used in both the on-state and the off-state thereof in the presence of low-band primary transmit signals, the on-state resistance RON and the off-state capacitance COFF of these switching elements must be balanced to minimize the generation of harmonics in both states. In other words, harmonic distortion in either one of the on-state and the off-state cannot be minimized at the expense of the other. This results in each one of the first antenna swapping switching element SW_AS1 and the second antenna swapping switching element SW_AS2 generating a moderate amount of harmonic distortion in both the on-state and the off-state thereof, and thus decrease the linearity of signals passed via the antenna swapping circuitry 14.
Accordingly, there is a need for RF front end circuitry with improved antenna swapping circuitry to increase linearity.